Overenthusiastic traction control?

F

Felixlamb

Member
Hey all,

Had my Z4 (20i) for nearly 3 months now. One of the annoying quibbles I’ve found is that the traction control seems to engage when I go over pretty much any speed bump. Even at a slow approach speed, the traction light still flashes for a good 2 seconds once I’ve come off the bump, and I lose power until the light turns off.

I guess this is intended? Even so, it feels like it’s way too sensitive for it’s own good, and I’ve found myself having to put the car into Sport+ just so I can pull away after the speed bumps.

Has anyone else experienced something similar to this?

Felix
 
Felixlamb said:
Hey all,

Had my Z4 (20i) for nearly 3 months now. One of the annoying quibbles I’ve found is that the traction control seems to engage when I go over pretty much any speed bump. Even at a slow approach speed, the traction light still flashes for a good 2 seconds once I’ve come off the bump, and I lose power until the light turns off.

I guess this is intended? Even so, it feels like it’s way too sensitive for it’s own good, and I’ve found myself having to put the car into Sport+ just so I can pull away after the speed bumps.

Has anyone else experienced something similar to this?

Felix
Click to expand...

Not noticed mine intruding on normal driving? :?
Rob
 
Mine does it on the sharp violent ones you get in Tesco car parks but not noticed it anywhere else, it also used to do it more when one of my tyre pressures were a little low due to a slow puncture.
 
It's more than likely the reluctor ring on the driveshaft. It's very well documented online and YouTube guides how to fix it, it's where the driveshaft rusts and bulges out the abs ring and it touches the sensor. It's happened to two of my z4s and is fixed by fitting new reluctor rings and new abs sensors if it's damaged them.

No need to disable a vital safety function which bmw provided in the first place, just get it fixed.
 
Could also be caused by changing the wheel and tyre sizes. If you change the rolling radius of one axle and not the other then that'll cause traction control to kick in more often and be less effective.
 
R.E92 said:
Could also be caused by changing the wheel and tyre sizes. If you change the rolling radius of one axle and not the other then that'll cause traction control to kick in more often and be less effective.
Click to expand...

I think politely that’s simply wrong...

The E89s have come with a wide variety of rim widths / diameters and associated tyres in many asymmetric combinations...it would course all sorts of issues if the car had to have some form of ‘balanced’ front /rear rolling radi


Traction control works in a straight line by comparing the relative speeds and the relative acceleration of the two driven wheels on the same axle.

The issue with a bump is that it temporarily unloads that wheel...a normal diff then spins that unloaded wheel faster by feeding almost all power to that unloaded wheel.

It takes a few seconds for the computers to stabilise this hence why the power is shut down first..that is in a straight line..different algorithms apply in corners..

My car does it quite badly for example on winter tyres on warm days when giving it serious beans..mine has been remapped..

On summer tyres in summer it does happen on hard acceleration on bumpy Scottish roads relatively easily..

I’m having a Quaif LSD flitted and will be interested to see how it checks out..
 
Pbondar said:
R.E92 said:
Could also be caused by changing the wheel and tyre sizes. If you change the rolling radius of one axle and not the other then that'll cause traction control to kick in more often and be less effective.
Click to expand...

I think politely that’s simply wrong...

The E89s have come with a wide variety of rim widths / diameters and associated tyres in many asymmetric combinations...it would course all sorts of issues if the car had to have some form of ‘balanced’ front /rear rolling radi


Traction control works in a straight line by comparing the relative speeds and the relative acceleration of the two driven wheels on the same axle.

The issue with a bump is that it temporarily unloads that wheel...a normal diff then spins that unloaded wheel faster by feeding almost all power to that unloaded wheel.

It takes a few seconds for the computers to stabilise this hence why the power is shut down first..that is in a straight line..different algorithms apply in corners..

My car does it quite badly for example on winter tyres on warm days when giving it serious beans..mine has been remapped..

On summer tyres in summer it does happen on hard acceleration on bumpy Scottish roads relatively easily..

I’m having a Quaif LSD flitted and will be interested to see how it checks out..
Click to expand...

Called Sytners yesterday who agreed that it seemed odd. Bought it from them in April so the car still has a good chunk of it's warranty time left so they are happy to look at it just for peace of mind. Just means another ball ache trying to sort out a courtesy car for a few days so I can get to work, which is extremely difficult when I'm only 19. Best call for the mother and her taxi services again! :rofl:
 
Pbondar said:
R.E92 said:
Could also be caused by changing the wheel and tyre sizes. If you change the rolling radius of one axle and not the other then that'll cause traction control to kick in more often and be less effective.
Click to expand...

I think politely that’s simply wrong...

The E89s have come with a wide variety of rim widths / diameters and associated tyres in many asymmetric combinations...it would course all sorts of issues if the car had to have some form of ‘balanced’ front /rear rolling radi


Traction control works in a straight line by comparing the relative speeds and the relative acceleration of the two driven wheels on the same axle.

The issue with a bump is that it temporarily unloads that wheel...a normal diff then spins that unloaded wheel faster by feeding almost all power to that unloaded wheel.

It takes a few seconds for the computers to stabilise this hence why the power is shut down first..that is in a straight line..different algorithms apply in corners..

My car does it quite badly for example on winter tyres on warm days when giving it serious beans..mine has been remapped..

On summer tyres in summer it does happen on hard acceleration on bumpy Scottish roads relatively easily..

I’m having a Quaif LSD flitted and will be interested to see how it checks out..
Click to expand...

Nice of you to be polite. But anecdotal evidence of you pootling around Scotland doesn't change anything.

There's 1 speed sensor per axle. Front and rear. On DCT cars there's also a shaft speed sensor that's used to manage torque output in the event of a traction event. Combined with yaw sensors these are the only inputs the car has to manage both traction and stability. Even a car without DCT will get screwed up by messing with the wheel speed calcs.

Increasing the rolling radius of one axle will make that speed sensor read lower than the other, that's not debatable. The stock sizes only have a 0.2% variance between front a rear speeds. I have upsized my wheels to 9j front and 9.5j rear but fitted the correct tyres to the car so my current variance is only 0.08%. If something stupid has been done, like increasing the rolling radius of the front tyres by 5% over the rear then you can expect problems.

You may be getting confused by wheel and tyre sizes. A car with 17" wheels from the factory will have the same rolling radius as a car with 19" wheels. The manufacturer will decrease the tyre height to compensate for the increase in wheel size.

You don't have to take my word for it that incorrect tyre sizes mess with electronics;
https://www.google.com/search?client=firefox-b-d&q=traction+control+tyre+sizes
 
R.E92 said:
Increasing the rolling radius of one axle will make that speed sensor read lower than the other, that's not debatable. The stock sizes only have a 0.2% variance between front a rear speeds.
Click to expand...

This does not seem right as a 255/30/19 tyre has a diameter of 635mm and from new to worn (8mm to 2mm tread left) the diameter will reduce by 2%, so if this was the case the traction light would be going mad if you had worn tyres on one axle and new ones on the other :?
 
keving1 said:
R.E92 said:
Increasing the rolling radius of one axle will make that speed sensor read lower than the other, that's not debatable. The stock sizes only have a 0.2% variance between front a rear speeds.
Click to expand...

This does not seem right as a 255/30/19 tyre has a diameter of 635mm and from new to worn (8mm to 2mm tread left) the diameter will reduce by 2%, so if this was the case the traction light would be going mad if you had worn tyres on one axle and new ones on the other :?
Click to expand...

It's proportional to the error. Tyre wear will be a tolerance factored into the design. Any error will increase the action of traction control. If the stock setup has a peak error of 2% due to wear then someone with something as minor as a profile increase at 1 axle will have an error of 7%.
 
If there is only one speed sensor on each axle, how does the system sense that one wheel is spinning on that axle?

I'm probably being a bit thick, but on a RWD car, I would have thought it more important to monitor the differences in rotational speed between the two rear wheels than to compare them with the front?
(Not withstanding the obvious difference when cornering).

What is it I am missing please?
 
OP. your not the only one, Mine does this when leaving my road. There are several of the annoying buggers up the road, and yes they do set the traction control off. But hey I don't neccessarily think this would be out of the ordinary at least on my speed bumps there is quite a shift in car weight etc. If it slows the car down temporarily then I deal with it.. There speed bumps there for a reason. ;)
 
enuff_zed said:
If there is only one speed sensor on each axle, how does the system sense that one wheel is spinning on that axle?

I'm probably being a bit thick, but on a RWD car, I would have thought it more important to monitor the differences in rotational speed between the two rear wheels than to compare them with the front?
(Not withstanding the obvious difference when cornering).

What is it I am missing please?
Click to expand...

There might well be 2 per axle. I read the BMW technical brief for the stability and traction control which mentions the sensors on each axle so that could have meant that there are 4 in total.
 
R.E92 said:
enuff_zed said:
If there is only one speed sensor on each axle, how does the system sense that one wheel is spinning on that axle?

I'm probably being a bit thick, but on a RWD car, I would have thought it more important to monitor the differences in rotational speed between the two rear wheels than to compare them with the front?
(Not withstanding the obvious difference when cornering).

What is it I am missing please?
Click to expand...

There might well be 2 per axle. I read the BMW technical brief for the stability and traction control which mentions the sensors on each axle so that could have meant that there are 4 in total.
Click to expand...

Fair enough. Thank you.
 
It's done from the ABS sensor ring - so one per wheel.

DSC is more complex than that though as it also takes inputs from throttle position, steering angle, yaw and longitudinal acceleration.
 
R.E92 said:
enuff_zed said:
If there is only one speed sensor on each axle, how does the system sense that one wheel is spinning on that axle?

I'm probably being a bit thick, but on a RWD car, I would have thought it more important to monitor the differences in rotational speed between the two rear wheels than to compare them with the front?
(Not withstanding the obvious difference when cornering).

What is it I am missing please?
Click to expand...

There might well be 2 per axle. I read the BMW technical brief for the stability and traction control which mentions the sensors on each axle so that could have meant that there are 4 in total.
Click to expand...


According to the E89 BMW USA technical briefing document to help the various traction /stability states there are:

4 wheel sensors sensing speed of each wheel
A longtitudinal acceleration sensor
Front and rear ride height sensors
Yaw angle sensor
Rate of change of steering sensor
Steering torque sensor
Torque sensor on gearbox output
On 8 speed boxes torque sensor on gearbox input

Some of which are duplicated and ignoring any just used for electronic damping..

As others suggested with only rotational sensor per axle you could not easily verify a spinning wheel in a straight line

The ABS system works in tandem and automatically calculates/ corrects for asymmetrical wheel arrangements

From a design viewpoint it would be a waste of assets not to make use of the abs wheel sensors since they are already there ..
 
Pbondar said:
R.E92 said:
enuff_zed said:
If there is only one speed sensor on each axle, how does the system sense that one wheel is spinning on that axle?

I'm probably being a bit thick, but on a RWD car, I would have thought it more important to monitor the differences in rotational speed between the two rear wheels than to compare them with the front?
(Not withstanding the obvious difference when cornering).

What is it I am missing please?
Click to expand...

There might well be 2 per axle. I read the BMW technical brief for the stability and traction control which mentions the sensors on each axle so that could have meant that there are 4 in total.
Click to expand...


According to the E89 BMW USA technical briefing document to help the various traction /stability states there are:

4 wheel sensors sensing speed of each wheel
A longtitudinal acceleration sensor
Front and rear ride height sensors
Yaw angle sensor
Rate of change of steering sensor
Steering torque sensor
Torque sensor on gearbox output
On 8 speed boxes torque sensor on gearbox input

Some of which are duplicated and ignoring any just used for electronic damping..

As others suggested with only rotational sensor per axle you could not easily verify a spinning wheel in a straight line

The ABS system works in tandem and automatically calculates/ corrects for asymmetrical wheel arrangements

From a design viewpoint it would be a waste of assets not to make use of the abs wheel sensors since they are already there ..
Click to expand...

The problem is that it doesn't adjust. Hence the plethora of topics across the likes of e90post stating that incorrect tyre sizes caused huge issues with traction control.
The E89 shares a platform with the E90 and has interchangeable control units and sensors.

If you upsize the tyres on one axle then the car will see the front wheels going at different speeds to the rear. It doesn't know the actual vehicle speed, it has to calculate it based off the wheels rotations.
 
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